Where they occur: Most common around the Pacific Rim

Max size: Largest ever recorded was 524m (1,720ft) high

Max speed: 800kmph (500mph)

Casualties: The current death rate for the 2004 Boxing Day tsunami disaster is 200,000

Tsunamis are giant waves that can wipe out entire coastal regions in minutes. They are caused by the motion of volcanic eruptions, earthquakes or massive landslides into the sea. For example, a huge column of water can be generated by an undersea earthquake, which gathers speed and height as it heads towards the shore. The shallower the water becomes, the bigger and faster the wave gets, until it is as tall as a skyscraper, travelling at the speed of a jetliner.

A tsunami will only stop when all its energy has been dissipated, so it can travel several hundred feet inland, scooping up boats, cars and other heavy debris and carry them inland.

On 26 December 2004, an earthquake occurred between the Australian and Eurasian plates in the Indian Ocean. The epicentre of the earthquake was about 160km (100 miles) from the western coast of Indonesia's Sumatra island. The earthquake triggered a Tsunami that devastated shorelines from Asia to Africa and has so far claimed the lives of over 200,000 people.